The subject matter disclosed herein relates generally to power system stabilization.
When a power system has a connection to a large utility network with many gigawatts of generated power, any individual electrical load on the power system will typically have only a negligible effect. In contrast, island power systems have no connection to a large utility network and island-like power systems have only a weak connection to a utility network (such as by means of a long transmission line with a comparably high impedance). Island and island-like power systems are commonly used in the marine industry (for example, onboard power systems of large ships), isolated on-shore installations, and the oil and gas industry. In such power systems, the balance between the power generated and the loads connected is more difficult to control, and voltage and frequency fluctuations are more frequently observed.
Disturbances in island and island-like power systems can cause instabilities that may lead to a system shutdown. Stabilizing measures or controls are used to improve system performance upon an occurrence of such disturbances. Types of such stabilizing measures or controls include transient stabilizers (such as fast acting switched braking resistors, mechanical power reduction systems, and intentional generation disconnection systems), dynamic stabilizers (such as variable conductance elements and control devices to modulate field voltage of synchronous generators), and combinations thereof. Transient stabilizers are used under (or after) fault conditions such as short circuits wherein the angular speed of one or more machines may increase with respect to the rest of machines in the system and thus cause a loss of synchronism. Dynamic stabilizers are used to address small signal problems that can be excited with disturbances related to switching operations during normal or contingency operation.
Under conventional approaches, when switched braking resistors are used, the dissipated power is difficult to control, and dynamic stability support is thus hard to achieve. Additionally, high voltage components (with nominal voltages greater than 1 kilovolt, for example) are used.
When dynamic stability improvement is attempted via generator excitation control, transient stability performance is often not noticeably enhanced.
A variable conductance, such as a dynamic braking resistor, is sometimes used for stabilizing a power system after a disturbance. Dynamic braking resistors typically comprise anti-parallel thyristors directly coupled to a power system busbar or coupled via a transformer. These approaches require damping power that is commonly achieved by embodiments including high-voltage devices.
It would be desirable to have a power system stabilizer suited for island and island-like power systems and capable of providing both transient and dynamic stability.